I've been playing on Aurora for a few months now, and I realized that at multiple occasion there was an emergency shuttle called for what could appear trivial matters.
The reasons I've seen to call an emergency evacuation shuttle have been from "The events caused psychological distress to the crew" to "Well nobody died but our security is not able to take control of the situation,” and there are plenty of others that I'm sure all of you have some examples of. (The examples given are a bit caricatural but they resume well the core of the reasons given.)
The reasoning, on the lore side, for a stricter guide line for the emergency shuttle is that NanoTrasen is a corporation in place for profit, and evacuating for anything other than the station being totally unfit to sustain life, the crew is totally unable to maintain reasonable research work (reasonable could be detailed here) or if it's overwhelmed without any chance to take back control by hostile forces, it will result in massive preventable income lost for NT. Any organization of that size won't let a costly action like that going on without pushing huge repercussion on the person that pulled the trigger.
Other reasoning for the gameplay part is that some person like the play in chaos from time to time, so having an end of the round forced at the first sign of a struggle when people still enjoy it seems a bit against the whole purpose of the game which is to have fun. But I understand there is some sort of balance to maintain to stay in the RP of the station, therefore the suggestion of clear criteria before arriving at an emergency shuttle situation. The idea of the proposition pretty much came to me when a shuttle was called seconds after an extension of the round vote passed for one of the reasons I've stated.
Of course, none of that applies to the transfer shuttle. If there is an end of the round vote passing, it's the end.
So in short, the idea would be to not be able / permitted to call an emergency shuttle unless:
Station is unfit to sustain life anymore
Station is unable to maintain reasonable research work
Station is overwhelmed by violent hostiles and there is no chance to take it back
Also, enabling people to play a bit more in chaos when it happens could eventually bring some new additions like "safe zone" or more escape pods.
Well, I hope my first post was clear enough, English is not my first language, so don't hesitate to ask questions if you need clarifications.